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S Sanvito

Publications and source records attributed to S Sanvito.

8 recordsLinked to original sources
PubMed2005

Conductance oscillations in zigzag platinum chains.

Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties of monatomic platinum chains, sandwiched between platinum electrodes. First, we demonstrate that the most stable atomic configuration corresponds to a zigzag arrangement that gradually straightens as the chains are stretched. Second, we find that the averaged conductance shows slight parity oscillations with the number of atoms in the chain. Additionally, the conductance of chains of fixed oscillates as the end atoms are pulled apart, due to the gradual closing and opening of conductance channels as the chain straightens.

Journal Article↗
PubMed2005

Self-interaction errors in density-functional calculations of electronic transport.

All density-functional calculations of single-molecule transport to date have used continuous exchange-correlation approximations. The lack of derivative discontinuity in such calculations leads to the erroneous prediction of metallic transport for insulating molecules. A simple and computationally undemanding atomic self-interaction correction (SIC) opens conduction gaps in I-V characteristics that otherwise are predicted metallic, as in the case of the prototype Au/ditholated-benzene/Au junction.

Journal Article↗
PubMed2005

Lattice distortion effects on the magnetostructural phase transition of MnAs.

We present a systematic experimental and theoretical study of the first-order phase transition of epitaxially grown MnAs thin films under biaxial tensile stress. Our results give direct information on the dependence of the phase-transition temperature of MnAs films on the lattice parameters. We demonstrate that an increase of the lattice constant in the hexagonal plane raises the phase-transition temperature (T(p)), while an increase of the perpendicular lattice constant lowers T(p). The results of calculations based on density functional theory are in good agreement with the experimental ones. Our findings open exciting prospects for magneto-mechanical devices, where the critical temperature for ferromagnetism can be engineered by external stress.

Journal Article↗
PubMed2005

Ferromagnetism driven by intrinsic point defects in HfO(2).

In view of recent experimental reports of unexpected ferromagnetism in HfO(2) thin films, we carried out first-principles investigations looking for magnetic order possibly brought about by the presence of small concentrations of intrinsic point defects. Ab initio electronic structure calculations using density functional theory show that isolated cation vacancy sites in HfO(2) lead to the formation of high-spin defect states. Furthermore these appear to be ferromagnetically coupled with a rather short range magnetic interaction, resulting in a ferromagnetic ground state for the whole system. More interestingly, the occurrence of these high-spin states and ferromagnetism is in the low symmetry monoclinic phase of HfO(2). This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.

Journal Article↗
PubMed2001

Ab initio transport theory for digital ferromagnetic heterostructures.

We present a theoretical density functional study of the electronic, magnetic, and transport properties of digital ferromagnetic heterostructures, obtained by delta doping GaAs with Mn. In the absence of intrinsic donors these systems have a half metallic density of states, with an exchange interaction much stronger than that of a random alloy with the same Mn concentration. Our ab initio ballistic transport calculations show that the carriers at the Fermi energy are strongly confined within a few monolayers around the MnAs plane. This strong confinement is responsible for the large exchange coupling and the two-dimensional half metallic behavior.

Journal Article↗
PubMed2000

Fractional quantum conductance in carbon nanotubes

Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].

Journal Article↗
PubMedDate not supplied

[Role of high resolution color-Doppler US of the sentinel node in patients with stage I melanoma].

PURPOSE: The aims of the present work are to assess the diagnostic accuracy of high resolution color Doppler ultrasound (US) of the sentinel node (SN) in patients with cutaneous melanoma skin at stage I. The US findings of nodal involvement could spare the patient a surgical step (selective lymphaderectomy) allowing them to undergo radical lymphadenectomy directly. MATERIAL AND METHODS: From November 1998 to November 2000 94 patients (mean age 52.7 years) underwent lymphoscintigraphy in order to mark the SN site on their skin. An US scan (112 lymphatic basins) was performed within 24 hours with a 10-13 MHz electronic linear probe with color-power-Doppler (Esaote AU5 Idea Scanner, Genoa, Italy). The sonographic features we analysed were: shape (roundness index), hilum displacement, intranodal heterogenicity, eccentric cortical thickness, extranodal invasion, vessel irregularity. RESULTS: 26 nodes showed US findings consistent with malignant involvement, 86 were negative. All the nodes were surgically removed and controlled by histology. Sensitivity and specificity of US scanning were 89.4% and 90.3%, the positive and negative predictive values 65.3% and 97.6%, respectively. US correctly identified the involved SN in 15,1% cases, so that 17 patients could have avoided the selective lymphadenectomy CONCLUSION: Preoperative lymphoscintigraphy and high-resolution color-Doppler US scanning constitute a useful diagnostic tool in identifying the metastatic SN, with a low margin of error. False negatives were technically induced, even using the more recent scanners, by the low US probe resolution, unable to recognise metastatic microdeposits. The two most reliable parameters in identifying involved lymphnodes were the roundness index and the absence of hilar echo. The advent of technologically more advanced probes should allow better spatial resolution and assessment of lymph node vascularization, enabling diagnosis of metastasis measuring less than 2 mm in diameter.

Adolescent↗